This invention relates to a separation process. In particular, it relates to separation of olefins from diolefins by extractive distillation.
Mixtures containing components of similar vapor pressures or components which tend to form azeotropes with one another are impossible to separate by simple distillation. Methods, such as azeotropic distillation, solvent extraction, adsorption on solids, and extractive distillation, have been proposed to achieve separation of these mixtures.
One separation which has caused considerable difficulty, is the separation of mixtures composed of olefins and diolefins, especially those having the same number of carbon atoms. To separate mixtures of olefins and diolefins, a third component, a selective solvent, can be added to the mixture to alter the relative volatility of the original constituents, thus permitting their separation. The term "relative volatility" (.alpha.), an indicator of separability of a mixture by distillation, can be expressed for binary mixture as: ##EQU1## WHERE X = MOLE FRACTION OF A in the liquid, and
Y* = MOLE FRACTION OF A in vapor; A being the more volatile component.
When .alpha. = 1, no separation is possible, and the larger the value of .alpha. above unity the greater the degree of separability. The selective solvent is usually of low volatility and is not appreciably vaporized in the fractionator. The selection of the solvent, for a particular system, is the crucial task in extractive distillation process.
The present invention provides a selective solvent for extractive distillation of a mixture comprising olefins and diolefins. Thus, one object of the invention is to provide an improved process for separation of mixtures of olefins and diolefins.
Another object of the invention is to provide a selective solvent for extractive distillation of a mixture including diolefins and olefins.
A further object of the invention is to provide an improved process for the removal of olefin impurities from a diolefin stream.
Still another object of the invention is to provide a solvent which is stable over wide range of temperatures.
Other objects of this invention will become apparent to those skilled in the art upon studying this disclosure.